What visa options do I have for a longer stay in Thailand without leaving the country?

@Be**

I'm not sure from your post whether you are extending each of your 30 day entries by another 30 days at immigration. Giving you 60 days stay on each occasion. If not you can extend that 30 day visa exempt entry at immigration for 1900baht. You can also extend that a further week for another 1900 baht which isn't really an extension but an order to leave in 7 days. Might be useful to match up with flights on occasion. This is not as economicacal as applying for a single entry tourist visa before you leave Australia, and extending that, more for if you're already in the country and want to stay

If you don't want that there's no really much you can do other than get a single entry tourist visa before you come here. That would stamp you in for 60 days when you arrive and you could get a 30 day extension on that for 1900baht at the immigration office. It'd take you to 90 days before you'd have to leave the country and either re-enter on a 30 day visa exempt entry or get a tourist visa from a thai consulate in a nearby country.

get a 6 month METV <- multi-entry tourist visa from the thai consulate in Australia before you come here. That visa will give you almost 9 months in country (in 60 day increments) if you need.